Refactor syscall_trace_enter() and syscall_trace_exit() to move thread
flag reading to the caller and adopt standard helpers. This aligns
arm64's internal tracing logic with the requirements of the generic
entry framework.

[Changes]
1. Function signature changes:
   - syscall_trace_enter(regs) → syscall_trace_enter(regs, flags)
   - syscall_trace_exit(regs) → syscall_trace_exit(regs, flags)

2. Move flags reading to caller:
   - Previously: read_thread_flags() called inside each function.
   - Now: caller (like el0_svc_common) passes flags as parameter.
   - Benefit: Avoids redundant flag reading and simplifies the interface.

3. Use syscall_get_nr() helper:
   - Replace direct regs->syscallno access with
     syscall_get_nr(current, regs).
   - This helper is functionally equivalent to direct access on arm64.

4. Re-read syscall number after tracepoint:
  - Re-fetch the syscall number after trace_sys_enter() as it may have
    been modified by BPF or ftrace probes, matching generic entry behavior.

5. Update syscall.c:
   - el0_svc_common() now passes flags to tracing functions and
     re-fetches flags before exit to handle potential TIF updates.

[Why this matters]
- Aligns arm64 with the generic entry interface.
- Makes future migration to generic entry framework.
- Properly handles syscall number modifications by tracers.
- Uses standard architecture-independent helpers.

No functional changes intended.

Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
---
 arch/arm64/include/asm/syscall.h |  4 ++--
 arch/arm64/kernel/ptrace.c       | 26 +++++++++++++++++---------
 arch/arm64/kernel/syscall.c      |  5 +++--
 3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index 5e4c7fc44f73..30b203ef156b 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -120,7 +120,7 @@ static inline int syscall_get_arch(struct task_struct *task)
 	return AUDIT_ARCH_AARCH64;
 }
 
-int syscall_trace_enter(struct pt_regs *regs);
-void syscall_trace_exit(struct pt_regs *regs);
+int syscall_trace_enter(struct pt_regs *regs, unsigned long flags);
+void syscall_trace_exit(struct pt_regs *regs, unsigned long flags);
 
 #endif	/* __ASM_SYSCALL_H */
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index ba5eab23fd90..8d296a07fbf7 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -2408,9 +2408,9 @@ static void report_syscall_exit(struct pt_regs *regs)
 	}
 }
 
-int syscall_trace_enter(struct pt_regs *regs)
+int syscall_trace_enter(struct pt_regs *regs, unsigned long flags)
 {
-	unsigned long flags = read_thread_flags();
+	long syscall;
 	int ret;
 
 	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
@@ -2423,19 +2423,27 @@ int syscall_trace_enter(struct pt_regs *regs)
 	if (secure_computing() == -1)
 		return NO_SYSCALL;
 
-	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
-		trace_sys_enter(regs, regs->syscallno);
+	/* Either of the above might have changed the syscall number */
+	syscall = syscall_get_nr(current, regs);
 
-	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
+	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) {
+		trace_sys_enter(regs, syscall);
+
+		/*
+		 * Probes or BPF hooks in the tracepoint may have changed the
+		 * system call number as well.
+		 */
+		 syscall = syscall_get_nr(current, regs);
+	}
+
+	audit_syscall_entry(syscall, regs->orig_x0, regs->regs[1],
 			    regs->regs[2], regs->regs[3]);
 
-	return regs->syscallno;
+	return syscall;
 }
 
-void syscall_trace_exit(struct pt_regs *regs)
+void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
 {
-	unsigned long flags = read_thread_flags();
-
 	audit_syscall_exit(regs);
 
 	if (flags & _TIF_SYSCALL_TRACEPOINT)
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index c062badd1a56..e8fd0d60ab09 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -124,7 +124,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 		 */
 		if (scno == NO_SYSCALL)
 			syscall_set_return_value(current, regs, -ENOSYS, 0);
-		scno = syscall_trace_enter(regs);
+		scno = syscall_trace_enter(regs, flags);
 		if (scno == NO_SYSCALL)
 			goto trace_exit;
 	}
@@ -143,7 +143,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	}
 
 trace_exit:
-	syscall_trace_exit(regs);
+	flags = read_thread_flags();
+	syscall_trace_exit(regs, flags);
 }
 
 void do_el0_svc(struct pt_regs *regs)
-- 
2.34.1